Method for catalytically heating wellbores

ABSTRACT

A catalytic heater is used in supplying heat to wellbores and has a catalytic surface open to the wellbore for contacting and causing the reaction of a fuel mixture. The preferable catalytic material is platinum supported on a matrix of asbestos, asbestosburlap, ceramic, or other non-combustible material. Air and fuel gas is injected into the wellbore to contact the catalyst. Initiation of a catalytic reaction is brought about by use of a fuel gas containing hydrogen which will spontaneously react with air at standard conditions in the presence of the catalyst. Once the hydrogen-air reaction reaches the reaction temperature of a hydrocarbon fuel gas and air, hydrogen injection is terminated. A carrier fluid may be used to transport the heat of reaction to a formation or other appropriate location.

Jan. 23, 1973 ilnited States Patent Berry et al.

xx am 6 6H 166 "66 m mm un e mm mflm ta en th anD om PSM 478 666 999 Ill 403 l 574 345 792 247 333 Dale W. Zadow, all of Richardson, Tex.

Primary Examiner-Stephen J. Novosad Attorney-George L. Church, Donald R. Johnson, Wilmer E. McCorquodale, Jr. and John E. Holder [73] Assignee: Sun Oil Company, Dallas, Tex.

Filed: Nov. 25, 1970 Appl. No.: 92,836

[57] ABSTRACT A catalytic heater is used in supplying heat to well- Related US. Application Data bores and has a catalytic surface open to the wellbore for t ct' and c sin th acti f a f l m [63] Continuation-in-part of Ser. No. 889,059, Dec. 30, con a mg au g 6 re on o ue IX 1969, abandoned.

ture. The preferable catalytic material is platinum supported on a matrix of asbestos, asbestos-burlap, ceramic, or other non-combustible material. Air and fuel gas is injected into the wellbore to contact the catalyst. Initiation of a catalytic reaction is brought about by use of a fuel gas containing hydrogen which will spontaneously react with air at standard condi- 04 2 6 0 33 B 64 6 m sm 2 L SE n 6 U r 6011 1 6 m m m0 6 mmh a... ma U l m l .m mm UIF 1. 2 8 555 tions in the presence of the catalyst. Once the hydrogen [56] References Cited UNITED STATES PATENTS -air reaction reaches the reaction temperature of a hydrocarbon fuel gas and air, hydrogen injec- 166/261 tion is terminated. A carrier fluid may be used to transport the heat of reaction to a formation or other appropriate location.

166/251 10 Claims, 3 Drawing Figures ......166/25i MacSporran.........................

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sum 2 or 2 INVENTOR DALE W. ZADOW HOLLAND J. BERRY ILL'IAM. C. HARDY ATTORNEY METHOD FOR CATALYTICALLY HEATING WELLBORES BACKGROUND OF THE INVENTION This application is a continuation-in-part of Ser. No. 889,059, filed Dec. 30, 1969, now abandoned, entitled CATALYTIC IGNITION F EARTH FORMA- TIONS.

This invention relates to a catalytic heater for use in supplying heat to a wellbore, and is related to two copending applications filed of even date with Ser. No. 889,059, entitled METHOD AND APPARATUS FOR IGNITION AND HEATING OF EARTH FOR- MATIONS, Ser. No. 889,061, now U.S. Pat. No. 3,680,636, and METHOD AND APPARATUS FOR IGNITING WELL HEATERS, Ser. No. 88,060, now U.S. Pat. No. 3,680,635. Several methods have been employed for heating wells for wellbore clean-out, sand consolidation, in situ combustion, etc. These methods have included downhole electrical heaters, gas burners and catalytic reactors. Air is flowed down the annulus of the oil well and its temperature is raised by the heater which is supplied with a fuel gas in the case of the gas burner and catalytic reactor. Electrical energy in lieu of fuel gas is used in the electrical heater.

The use of electrical heaters has been limited to shallow wells due to the difficulty related to supplying adequate electrical power at depths in excess of 3,000 feet. High voltages are required for operation of the electrical heater and when the electrical cable exceeds about 3,000 feet, the resistance in the cable reduces the downhole voltage below that required for operation of the electrical heater. Also, the electrical heaters have a tendency to short out owing to hot spots developing through poor heat exchange resulting from coke formation on its surface. The temperature in this coke layer will build up until it exceeds the melting point of the heating elements, causing the electrical heater to fail. Additionally, a source of electrical energy is not always available in remote areas, which necessitates use of a large generator.

The drawbacks related to gas fuel burners relate to damage to well equipment because of the high combustion temperature of natural gas which can approximate 4,000 F. At this temperature, theheat shield, tubing, and casing may be damaged, especially if the flame stands off from the nozzle where the fuel gas exits. When a stand-off flame extends below the heat shield for an appreciable period of time, the unprotected casing will be damaged and if the wellbore is uncased, formation permeability may be damaged in the vicinity of the wellbore.

In the case of both gas burners and catalytic reactors, there are problems related to ignition of the burner or commencement of the catalytic reaction. Currently, gas burners are being ignited by pyrophoric chemicals which necessitates purging the tubing of air with nitrogen, since such chemicals ignite in the presence of air at standard conditions. The pyrophoric chemical is lowered to the burner where it contacts a mixture of fuel gas and air which will explode if the mixture is too rich, and will not ignite if too lean. Irreparable well damage can result from an explosion, and the tedious purging procedures must be repeated if the burner fails to ignite due to a lean mixture.

Catalytic heaters are known in the art; however, ignition temperatures of the fuel gases employed required an external source of heat. This heat has been provided by preheating the fuel gas or by heating the catalytic surface itself. A propane-air fuel mixture requires fuel preheating of at least 600 F. for its reaction at the catalytic surface; and a methanol-air fuel mixture requires preheating to at least 200 F. Additionally, present catalytic heaters are enclosed systems requiring expensive equipment and resulting in inefficient heat exchange to the formation. It is therefore an object of the present invention to provide an improved downhole catalytic heater and method of initiating the catalytic reaction.

SUM MARY OF THE INVENTION With these and other objects in view, the present invention contemplates use of a catalytic downhole heater completely open to the interior of the wellbore and/or arranged in a heat shield having air inlets with adjacent baffles for imparting turbulence to air entering the heat shield. This heater is initiated by injection of a fuel mixture comprising hydrogen and natural gas in a volumetric ratio of approximately 1 to 4, respectively. Also it can be initiated by using a wireline operated electrical system which provides heat to a heating element built into the catalytic heater.

Alternatively, catalytic material is placed in the wellbore adjacent a formation or area being heated, so that the fuel gas would flow through the catalytic material on its way to the formation or other area. Also, powderized catalytic material may be carried into a formation adjacent the wellbore by air injected into the formation. A complete understanding of this invention may be had by reference to the following detailed description, when read in conjunction with the accompanying drawings illustrating embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a catalytic heater located in a downhole position seated inside a heat shield;

FIG. 2 is a cross section along lines 22 of the catalytic heater of FIG. 1; and

FIG. 3 is a cross-section of catalytic material placed in the wellbore, opposite a formation being heated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 of the drawings, there is seen a retrievable catalytic heater located in a wellbore. The heater 38 is located inside of and extending through the tubing 14 with the lower end having a catalytic surface 40 surrounded by an open bottomed heat shield 26. The heat shield is attached to the tubing 14 by attachment members 20. This heat shield 26 is optional as will be better understood hereinafter.

Baffles shown at 58 in FIG. 2 are adjacent to the attachment members 20. The heater 38 shown in FIG. 1 is rested on seating nipple 54 which contacts the no go" flange 28 of the heater 38. An O-ring seal assembly 52 is employed to seal the heaters catalytic exterior 40 from the tubing interior.

The upper portion of the heater 38 has a cable head and thermocouple hanger assembly 24 for connecting a double armored high temperature thermocouple cable 16. The hanger assembly 24 is positioned above the no go flange 28 and is separated therefrom by upper stand-off member 32. The upper stand-off member 32 has gas inlet ports 22 which are channels extending through the side wall of the stand-off member 32. Gas flows to the interior of the heater 38 through upper stand-off member 32, seating nipple 54, lower stand-off 34 and gas distribution tube 44. Tube 44 extends through the catalytic portion of the heater 38. The catalytic portion of the heater 38 comprises catalytic material on a support having a surface 40 held by heater screen 36. A fiberized silica material 42 such as FIBERGLASS or CERAFELT is located between the distributor tube 44 and the catalytic surface 40. The supported catalytic material is arranged so that spaces are present between the particles of the catalytic material and therefore the material defines fluid flow passageways. Located on the catalytic surface is a skin thermocouple 46 which is connected to the thermocouple cable 16.

Attached to the lower end of the catalytic portion of the heater is a sub 70, housing a temperature pill holder 50 and a hot air thermocouple 48. The hot air thermocouple 48, like the skin thermocouple 46 is connected to the thermocouple cable 16. These thermocouples transmit an electromotive force signal which is carried by the thermocouple cable 16 to an indicator located at the surface (not shown).

' To ensure that the tubing 14, heat shield 26, and heater 38 are properly positioned in the casing 12, centralizers 68 are attached to the exterior of the tubing 14 just above the top of the heat shield 26.

In the operation of this heater one component of a fuel mixture (usually air) is passed down the annulus between tubing 14 and casing 12. The remaining portion of the fuel mixture (usually a hydrocarbon gas) is flowed down the tubing interior, passes through fuel passages 22 to enter gas distributing tube 44 located in the interior of the heater 38. This remaining portion of the fuel mixture then flows down distributing tube 44; enters the catalytic portion of the heater 38; passes through perforations in the wall of the distributing tube 44; enters the area occupied by the silica material 42; contacts the catalytic material; and exits the heater 38 by passing through the catalytic surface 40. Since the component of the fuel mixture descending the annulus enters the heat shield 26 by way of air inlets 18 it comes into contact with the catalytic surface 40 and the complete fuel mixture is available for reaction.

When the heater 38 is being used for heating a formation 56 adjacent the wellbore, a gas is initially pumped into the formation to force reservoir fluids away from the wellbore. After these reservoir fluids have been cleared from the wellbore and adjacent formation, fuel gas is injected into the tubing 14 and passes through fuel passages 22 to enter gas distributing tube 44 located in the interior of the heater 38.The gas flows down tube 44 and enters the catalytic portion of the heater 38. The fuel gas is diffused by the baffling action of the fiberized silica material 42, and contacts the catalytic material, whereupon it exits the heater 38 by passing through catalytic surface 40. The fiberized silica material CERAFELT has excellent heat resistant properties which are desirable in this use. Upon exiting the catalyst the fuel gas is in communication with the injected air which enters the heat shield 26.

To initiate the catalytic reaction, a fuel gas is used preferably comprised of natural gas and hydrogen in a 4:1 ratio. A hydrogen slug preceding the natural gas can also be employed as well as ratios of natural gas to hydrogen from 1:1 to 10:1. In the presence of a catalytic material such as platinum, the hydrogen will react with air at temperatures in excess of approximately 20 F. The hydrogen air reaction will raise the temperature in excess of the catalyzed reaction temperature of natural gas and air which approximates 250 F. Once the natural gas and air react, the hydrogen portion of the fuel gas is no longer needed. Indications of the natural gas-air reaction is derived from the information transmitted by the skin thermocouple 46 and hot air thermocouple 48.

Another method of initiation of a catalytic reaction of natural gas and air is by heating the catalytic heater with a battery powered ignitor supplying energy to a heating coil located adjacent the heater.

Utilization of the hydrogen-natural gas fuel mixture besides providing spontaneous ignition of the heater, also allows a high fuel injection rate and makes the possibility of an explosion less likely than if pure hydrogen is used. If hydrogen alone were used only about 6 cubic feet of hydrogen per hour per square foot of catalyst surface could be injected. With a natural gas-hydrogen mixture, injection rates can be increased to 20-25 standard cubic feet per hour per square foot of catalyst surface. After initiation of the natural gas-air reaction and cessation of the injection of the hydrogen portion of the fuel, the fuel injection rate should be supplied at the rate of 20-45 SCF/hr/ft of catalyst surface, depending on heat requirements and information received from the thermocouples 46 and 48.

In an in situ combustion operation, air flowing inside the heat shield entering through inlets 18 is divided between air entering .into the reaction with the catalyzed fuel gas, and air which acts as a carrier of the heat generated by such reaction. This heat carrier air upon exiting the heat shield mixes with the air flowing down the annulus which does not enter the heat shield. This mixing raises significantly the temperature of the entire air stream entering the formation 56.

The hot air thermocouple 48 is located below the heat shield in order to be exposed to the air stream consisting of heat carrier air and air flowing through the annulus 13. The thermocouple 48 thus would be indicative of the temperature of the air entering the formation 56. The baffles 58 shown in FIG. 2 located adjacent the upper air inlets l8 ensure a turbulent air stream for contacting the natural gas-air reaction and for mixing with the air flowing down the annulus 13 which does not enter the heat shield.

The temperature pill holder 50 is located adjacent the hot air thermocouple 48 and contains pills which melt at different temperatures so that the highest temperature attained can be determined. Accurate temperature information is important in determining whether the thermocouple 48 is transmitting accurate information. Also, in case of damage to the well caused by excessive downhole heat, the pills could be used to determine the highest temperature attained for analysis of the causes of damage.

If the natural gas-air reaction should go to flame, temperatures approximating 4,000 F. could be reached, and if that temperature were reached for any appreciable time period, damage to downhole equipment would result. Accordingly, the reaction should not be allowed to go to flame, and preferably would be maintained at a level below 1,000 F. This would be several hundred degrees below the temperature that the reaction would go to flame, thereby affording a substantial safety factor. Because the temperature is kept below that which would cause damage to well pipe, the heat shield 26 is not necessary.

To prevent an explosive mixture of air and fuel gas, the air to fuel ratio should be in the range of 30:1 to 60:1. An explosive mixture of methane is 5 to percent methane by volume with the remainder air and the explosive range for hydrogen is 4 to 74 percent hydrogen by volume. Therefore, an explosive mixture will be avoided if the air to fuel ratio is at least 25 to 1.

If the thermocouples indicate that the reaction has gone to flame, it can be quickly snuffed out by cutting back on the fuel injection rate. It has been observed that the downhole temperature decreases rapidly in response to a cut back in fuel and increases at a much slower rate when the fuel injection rate is increased. It would therefore be expected that the operation could be at least partially automated with injection rate controls acting in response to thermocouple information. An alarm system would be necessary in a semi-automated system when excessive temperatures are reached.

FIG. 2 is a cross-section along lines 2-2 of the heater and heat shield shown in FIG. 1. The tubing 14 is located inside of the casing 12 with a heat shield 26 attached to the lower portion of the tubing by attachment members 20. Air inlets 18 are located in the wall of the heat shield 26. The baffles 58 are arranged so as to impart turbulence to the air entering upper air inlets 18.

This turbulent air flow insures a complete reaction of the air and fuel gas on the catalytic surface of the heater 38 as well as diminishing the likelihood of hot spots developing inside the heat shield 26.

The catalytic material used may be selected from a wide list of materials and form no part of this invention. The preferable catalyst is platinum on a heat resistant support such as asbestos or ceramic material. Other catalysts suitable for oxidation of the fuel gas used herein include the platinum group metals and their oxides. Many other catalytic materials may be used in this reaction and are well known to those of average skill in the catalytic art.

The outside diameter of the catalytic heater 38 is smaller than the inside diameter of the tubing 14 allowing running and retrieval by wireline. The gas distributing tube 44 carries fuel gas to the catalytic area of the heater 38 where the fuel gas enters numerous small openings in the gas distributing tube 44 and contacts the fiberized silica material 42 such as CERAFELT which operates to disperse the fuel gases that it contacts a broader area of the catalytic surface 40. The fiberized silica 42 is arranged such that there is only a slight pressure drop as the fuel gas exits the heater 38. The heater screen 36 acts as a retainer for the supported catalytic material and provides a rigid shape to the catalytic area of the heater 38 so that it is not easily deformed.

Alternatively, a catalyst such as platinum oxide together with a support material such as aluminum silicate can be homogeneously formed in the shape of a hollow cylinder. The exterior of the cylinder may be sprayed with a cohesive agent such as sodium silicate to prevent fragmentation or crumbling. This heater construction affords a more effective fuel contact and elimination of the need for dispersing material 42 or heater screen 36, since the catalyst and support, together with a gas distributing tube 44, possesses sufficient rigidity to withstand wellbore running and retrieval.

FIG. 3 is illustrative of a system for heating a formation without need for special downhole equipment. Most wells have casing 12 and tubing 14 located in the wellbore although neither is essential to the operation described herein. The formation location should be fairly accurately determined as well as the area in the wellbore below the formation. lf liquids are present in the wellbore they should be bailed out. Coarse sand 60 of approximately 12 to 60 mesh is injected into the wellbore in a volume approximating the volume of the wellbore located below the formation to be ignited. Air

is then pumped down the wellbore into the formation to be ignited at a rate sufficient to free the wellbore and formation 56 adjacent the wellbore, of fluids.

When the wellbore and adjacent formation 56 are freed of fluids, a catalytic material 62 supported on ceramic aggregate is injected into the wellbore in sufficient quantity to fill the wellbore adjacent the formation 56. A gas is continually pumped into the formation during the placement of the catalyst as the catalyst should be kept free from liquids to prevent contamination.

A fuel mixture containing hydrogen is then injected into the wellbore together with air. It is preferable to inject the fuel mixture into the tubing 14 and the air into the annulus 13 so that a combustible mixture is not present until the bottom of the wellbore is reached. Air injected at high pressure can become very hot at points of anomaly interposed in its path, thus causing ignition under certain circumstances.

Upon the fuel mixture reaching the catalytic material 62 on its path to the formation 56 the hydrogen spontaneously reacts with the air since the reaction temperature is around 20 F. When the reaction temperature of hydrogen and air reaches approximately 250 F., natural gas will react. Once the natural gas or other fuel has started to react, the hydrogen portion of the fuel is no longer needed. When heat is being supplied to the formation to initiate in situ combustion of formation fluids, production and pressure at adjacent producing wells can be monitored to determine when such combustion has commenced. Once commenced, the fuel gas is no longer needed.

The catalytic aggregate should be sized so that the passageway into the formation is not blocked or is not so blocked as to create a significant back pressure. Aggregate a quarter to a half inch in diameter should serve well in this regard. The points of contact between adjacent catalytic aggregate defines air flow channels for the air entering the formation. Such a formation ignition procedure has the advantage of dispensing with downhole hardware and its related cost. The tubing need not be pulled to attach a seating nipple and heat shield. The catalytic material is readily available and inexpensive and therefore may be left in the wellbore or removed without regard to contamination.

In order to monitor the operation of this formation ignition procedure, a thermocouple is lowered on a high temperature thermocouple cable until it contacts the catalyst bed. Readings taken from the thermocouple would indicate whether a reaction was in process and if the injection rates should be modified to effect a temperature change.

Another method of catalytically igniting the formation is to operate in essentially the same manner described in the description of FIG. 3 up until injection of the catalytic aggregate. Those steps would be: the wellbore liquid removal, and gas injection to force the formation fluid away from the wellbore.

In lieu of injecting catalytic aggregate in the wellbore adjacent the formation, a powdered catalyst would be injected into the gas stream to be carried into the formation. A hydrogen containing fuel gas would then be injected to initiate a catalytic reaction. Once the temperature was raised to allow catalytic reaction of natural gas or other fuel, the hydrogen portion would be deleted. It should be noted that this process is essentially the same as that described in the description of FIG. 3, except that a powdered catalyst is carried into the formation by flow of the injected gas rather than remaining in the wellbore as would be the case for the catalytic aggregate.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A process of initiating in situ combustion of earth formation hydrocarbons penetrated by a wellbore com- 7 prising the steps of: locating a catalytic material in the earth formation adjacent the wellbore; flowing a fuel mixture containing hydrogen and air into the earth formation and into contact with the catalytic material thereby causing a catalytic reaction of the hydrogen and air; flowing a fuel mixture containing a hydrocarbon and oxygen into the earth formation and into contact with the catalyst until combustion of formation hydrocarbons occurs.

2. The process of claim 1 wherein the hydrocarbon being flowed into the earth formation includes natural gas and wherein the catalytic material placed in the earth formation includes a platinum group catalyst.

3. The process of claim 1 including the step of terminating the flow of the hydrocarbon into the formation subsequent to initiation of combustion of formation hydrocarbons.

4. The process of claim 1 wherein the catalytic material is located in the earth formation by flowing the catalytic material into the formation in a powderized form carried in a gaseous medium.

5. A process of supplying heat to an earth formation containing liquid hydrocarbons and penetrated by a wellbore comprising the steps of: flowing a gas into the earth formation; injecting a powderized catalyst into the gas stream so that it is carried into the earth formation adjacent the wellbore' injectin a hydrogen and oxygen containing gas into the earth ormation and into contact with the catalytic material to cause a hydrogenoxygen catalytic reaction in order to elevate the temperature adjacent the catalytic material above the catalytic reaction temperature of natural gas and air; and simultaneously with the hydrogen-oxygen injection, injecting natural gas into the earth formation which reacts with oxygen at such time as the temperature adjacent the catalytic material reaches the reaction temperature of the natural gas and air.

6. The process of claim 5 wherein the hydrogen injection is terminated subsequent to initiation of the natural gas and oxygen reaction and wherein natural gas injection is terminated subsequent to in-situ combustion of formation hydrocarbons.

7. The process of claim 6 including the step of monitoring the temperature in the wellbore adjacent the earth formation to determine the occurrences of the hydrogen-oxygen catalytic reaction and the natural gas-oxygen catalytic reaction.

8. The process of claim 5 wherein hydrogen and natural gas injection is terminated subsequent to initiation of in-situ combustion of formation hydrocarbons.

9. The process of claim 5 wherein the oxygen injected into the formation is provided by injecting air into the earth formation.

10. The process of claim 5 wherein the oxygen is injected into the earth formation by one conduit and the natural gas and hydrogen are injected into the earth formation by a separate conduit. 

2. The process of claim 1 wherein the hydrocarbon being flowed into the earth formation includes natural gas and wherein the catalytic material placed in the earth formation includes a platinum group catalyst.
 3. The process of claim 1 including the step of terminating the flow of the hydrocarbon into the formation subsequent to initiation of combustion of formation hydrocarbons.
 4. The process of claim 1 wherein the catalytic material is located in the earth formation by flowing the catalytic material into the formation in a powderized form carried in a gaseous medium.
 5. A process of supplying heat to an earth formation containing liquid hydrocarbons and penetrated by a wellbore comprising the steps of: flowing a gas into the earth formation; injecting a powderized catalyst into the gas stream so that it is carried into the earth formation adjacent the wellbore; injecting a hydrogen and oxygen containing gas into the earth formation and into contact with the catalytic material to cause a hydrogen-oxygen catalytic reaction in order to elevate the temperature adjacent the catalytic material above the catalytic reaction temperature of natural gas and air; and simultaneously with the hydrogen-oxygen injection, injecting natural gas into the earth formation which reacts with oxygen at such time as the temperature adjacent the catalytic material reaches the reaction temperature of the natural gas and air.
 6. The process of claim 5 wherein the hydrogen injection is terminated subsequent to initiation of the natural gas and oxygen reaction and wherein natural gas injection is terminated subsequent to in-situ combustion of formation hydrocarbons.
 7. The process of claim 6 including the step of monitoring the temperature in the wellbore adjacent the earth formation to determine the occurrences of the hydrogen-oxygen catalytic reaction and the natural gas-oxygen catalytic reaction.
 8. The process of claim 5 wherein hydrogen and natural gas injection is terminated subsequent to initiation of in-situ combustion of formation hydrocarbons.
 9. The process of claim 5 wherein the oxygen injected into the formation is provided by injecting air into the earth formation.
 10. The process of claim 5 wherein the oxygen is injected into the earth formation by one conduit and the natural gas and hydrogen are injected into the earth formation by a separate conduit. 